"Regrettably, we've found that China has been attempting to interfere in our upcoming 2018 election, coming up in November, against my administration," Trump told the Security Council on Wednesday at a meeting he hosted.

"They do not want me or us to win because I am the first president ever to challenge China on trade and we are winning on trade, we are winning at every level. We don't want them to meddle or interfere in our upcoming election."

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He did not present evidence for the assertion but a tweet he posted shortly afterward suggested he was basing the accusation on the Iowa newspaper ad.

While US national security officials are at high alert for an attempt at election interference by a foreign adversary, Russia has been seen as a more likely threat than China.

"We do not and will not interfere in any country's domestic affairs," Chinese Foreign Minister Wang Yi said at the Security Council meeting, through a translator. "We refuse to accept any unwarranted accusations against China."

Donald Trump has accused China of trying to interfere in US midterm elections.Credit:AP

Dan Coats, the director of US national intelligence, told reporters on September 12 that China was one of several countries with "capabilities" to interfere in the elections. "It's more than Russia here that we're looking at," he said. But he did not allege that Beijing had taken any action.

Trump has slapped tariffs on $US250 billion ($343 billion) in Chinese goods as part of an escalating trade war between the two countries, and several of his advisers said he was likely referring both to Chinese counter-tariffs that have targeted politically sensitive industries - especially in Midwest states Trump won - as well as the Chinese public relations campaign.

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On Sunday, the Chinese government bought a four-page advertising supplement in the Des Moines Register, Iowa's largest newspaper, to highlight the impact of the trade war on the state's soy farmers. The supplement called the dispute "the fruit of a President's folly".

The US intelligence community concluded that Russia interfered in the 2016 election with a covert social media campaign intended to help Trump win. He has grudgingly accepted the conclusion but insists the meddling didn't assist his campaign.